Grain size dependence of the γ→α martensite transformation starting temperature

Abstract

In the work, a dependence of the γ→α a martensite transformation starting temperature on the grain size D is derived. A formula for the critical grain size Dc is proposed reflecting the effect of physical parameters on Dc; among the parameters are the group velocity vs and the attenuation Γs for s-electrons, the ratio of spatial scales characteristic of martensite crystal nucleation in the elastic field of an individual dislocation, and the energy range critical for the selection of pairs of active electronic states. With D<Dc, the martensite transformation is suppressed, Ms (Dc)=0. In the framework of dynamic theory, Ms is identified with the optimum temperature at which nonequilibrium d-electrons generate waves responsible for the growth of martensite crystals. It is shown that the Γs dependence of Dc is singular and allows explanation of the existence of concentration boundaries of alloying elements. Comparison is made between the obtained results and available experimental data. © 2010.